Quantum dots are semiconductor nanocrystals whose particle sizes are smaller than their Bohr radiuses (about 10 nm). Due to discrete energy states of the quantum dots, motion of conduction band electrons and valence band holes are confined in a three-dimensional potential well, which leads to unique physical properties. With the quantum size effects, optical and electrical properties of a quantum dot can be flexibly tuned by adjusting its size, which facilitate the infrared light absorption and emission of inorganic quantum dots compared with traditional organic light absorbers. In addition, low-cost preparation of semiconductor devices, especially those flexible devices with plastic substrate, can be achieved by preparing quantum dot films via cheap process such as printing or roller coating, from quantum dot colloidal solution formed by dispersing quantum dots in a solvent. With such characteristics, quantum dots exhibit attractive and broad application prospects in various technical fields, such as novel light-emitting diodes (LEDs), efficient and low-cost stacked solar cells, infrared light detectors, semiconductor lasers, and biological fluorescence imaging.
As CuInS2 quantum dots are free of heavy metals and non-toxic, they become research hotspots in the field of fluorescent quantum dots. However, the fluorescence quantum yields of CuInS2 quantum dots are low, generally below 10%. In order to improve the fluorescence quantum yield of the CuInS2 quantum dots and enhance the photochemical stability thereof, some techniques have been developed including constructing alloy quantum dots such as ZnCuInS2, and constructing quantum dots with core-shell structure such as CuInS2/CdS and CuInS2/ZnS. However, the CuInS2/CdS comprises cadmium, and the CuInS2/ZnS involves a blue shift in fluorescence emission which leads to a lower quantum yields of dots in red region.